I. Introduction
Among various renewable energy sources, photovoltaic (PV) generation is getting attractive because it is superior to other power sources in terms of technology and economy. Since a PV module generates a dc power, a dc-ac inverter is essentially required. A microinverter is attached to the back side of a PV module and directly transfers the power generated by the module to the grid. To maximize the power generation capability from the PV module, the microinverter should be highly efficient as well as securing accurate maximum power point tracking performance. Either isolated or non-isolated microinverter can be configured with a PV panel. Compared to non-isolated microinverters, isolated microinverters can mitigate the leakage current problem which may cause critical safety issues in the industrial field. Fig. 1 compares two types of isolated microinverter configurations, single and two-stages. A single-stage configuration may be advantageous to maximize a peak efficiency at a certain condition, but it will be hard to implement grid support function. On the other hand, a two-stage configuration may be difficult to secure a high CEC efficiency because it requires several components. However, it can be overcome with a high degree of freedom in implementing advanced control strategies. In addition, it is also suitable for the implementation of grid support functions which is getting important recently. Hence, this paper focuses on the efficiency optimization of a two-stage microinverter.